#include <iostream>
#include <map>

using std::cout;
using std::endl;
using std::map;

class Example
{
public:
/*     bool operator()(const Example &lhs, const Example &rhs) const */
/*     { */
/*         return 1; */
    /* } */
    int _ix;
};

bool operator<(const Example &lhs, const Example &rhs)
{
    return lhs._ix <= rhs._ix;
}

void test()
{
    Example ex;
    map<Example, int> number = {
        {ex, 10},
        {ex, 20},
    };

    cout << "size() = " << number.size() << endl;
}

int main(int argc, char *argv[])
{
    test();
    return 0;
}

